1. Technical Field of the Invention
The present invention relates to disk drives and read and write channel coding.
2. Description of Related Art
As is known, many varieties of disk drives, such as magnetic disk drives are used to provide data storage for a host device, either directly, or through a network such as a storage area network (SAN) or network attached storage (NAS). Typical host devices include stand alone computer systems such as a desktop or laptop computer, enterprise storage devices such as servers, storage arrays such as a redundant array of independent disks (RAID) arrays, storage routers, storage switches and storage directors, and other consumer devices such as video game systems and digital video recorders. These devices provide high storage capacity in a cost effective manner.
A typical magnetic disk drive uses a read/write head that operates via longitudinal magnetic recording. Data to be written on the disk is run-length limited (RLL) coded to limit the number of sequential 0's in the bitstream to attenuate the DC response of the signal that is read back from the disk. The RLL coding allows very high code rates with relatively low complexity. The RLL coded bitstream is coded again with an error correcting code, prior to writing the data, in order to correct errors that can occur in read/write operations.
A sizable market has developed for these devices and the price per unit of storage has steadily dropped. Modern host devices are provided with greater storage capacity at reduced cost, compared with devices that where manufactured a few years earlier. The need exists for efficient disk drives that can store and retrieve data with greater accuracy and at greater density.